February 14, 2008

Few French Fried in 2006

In the history of global warming scare stories, the 2003 European heat wave was a landmark event—it was the first time that a rash of human deaths were specifically linked to global warming. Many of you probably recall that a widespread exceptionally hot and dry spell hit Western Europe in August, 2003. Depending on how you count the bodies, up to 35,000 people suffered premature death during this heat wave with the lions-share occurring in France, which happened to be heat wave ground zero. Subsequent research demonstrated that this kind of extreme heat event must surely have been caused by increased greenhouse gas levels (Schår et al., 2004), despite the fact that, when examined from a global perspective, this heat wave was very Euro-centric (Chase et al., 2006), and the last time we checked a map, western Europe doesn’t cover much of the globe (which of course is the reason for centuries of European colonialism).

Well, we bet you didn’t know that there was a very comparable heat wave in France in summer, 2006. Why no headlines about global warming’s increasing death toll? In the category of “all the news that’s apparently not fit to print,” you guessed it, many fewer people died. The 2006 heat wave is the subject of a recent paper in the International Journal of Epidemiology by a group of French researchers led by A. Fouillet entitled, “Has the impact of heat waves on mortality changed in France since the European heat wave of summer 2003? A study of the 2006 heat wave.”

Fouillet and colleagues began by developing a model in which they used temperature data to predict daily summer mortality rates over the historical record (1975–1999). There is a surprisingly strong relationship between temperatures and summer death rates (their overall model explained variance was 79%). For example, Figure 1 (below) shows minimum and maximum temperatures and mortality rates for June through August of 20006 (recall the European convention of date/month rather than month/date on the x-axis). It’s easy to visually track the linkage between the temperature and mortality lines. Note during mid–late July in particular, when the heat wave was going full blast, that mortality rates persisted at well over 7 daily deaths/100,000 population.


Figure 1. Observed daily mortality rate (deaths per 100,000 subjects; black line), maximum (red) and minimum (blue) temperatures (°C) in France in June–September, 2006.

Because of these very consistent linkages between temperature and mortality, the authors were able to statistically estimate the number of deaths expected based upon observed temperatures. Figure 2 (top) shows the predicted and observed values for the notorious summer of 2003. It’s not hard to find the heat wave in this graph. At the mortality peak, the model predicted about 17 deaths/100,000 but nearly 21 deaths/100,000 were observed. In other words, far more people died than would have been expected based on the observed temperatures.

Figure 2. Observed (black line), predicted (red line) and baseline (blue line) daily mortality (deaths/100,000 population) in France in summer, 2003 (top) and summer, 2006 (bottom).

In July, 2006, the situation was quite different (Figure 2, bottom). Now, the temperature model predicted far more deaths than actually occurred. Although there was a mortality spike (about 9% according to the authors), the model estimated almost 6500 excess deaths during the heat wave but only around 2000 occurred. Specifically, the death count was 4388 less than expected.

Can we attribute these saved lives to global warming? Well, maybe indirectly. In response to the tragedy of 2003, the French government implemented a National Heat Wave Plan that included “set-up of a system for real-time surveillance of health data, compilation of scientific recommendations on the prevention and treatment of heat-related diseases, air-conditioning equipment for hospitals and retirement homes, drawing up of emergency plans for retirement homes, city-scale censuses of the isolated and vulnerable, visits to those people during the alert periods, and set-up of a warming system.” In other words, France adapted to the heat wave by providing information to the population at-large and air-conditioning to the most vulnerable. No doubt people were also personally more aware of the dangers of summer heat in 2006 than they were three years earlier. In reality, while there is a consistent increase in deaths when summer temperatures rise, there is no excuse for mass heat-related mortality like what occurred in 2003 in any technologically-advanced country.

(It’s not often discussed (for obvious reasons), but the 2003 heat wave occurred in August, and anyone who’s traveled western Europe in August knows that it’s basically deserted, except for the Mediterranean beaches where just about every able-bodied Euro spends the month basking in the sun while leaving their less able-bodied relatives back home in sweltering apartments. The authors did factor monthly mortality trends into their study, but we still wonder what might have happened if the 2006 heat wave hit one month later…)

Let’s face it…the planet is warming and, short of China and India going green, there’s nothing anybody can do about it (go ahead and install energy-saving light bulbs, but that ain’t going to change global temperatures). It would be foolish to argue that we’re not going to see more and longer summer heat waves as greenhouse gas levels continue to increase. But that certainly doesn’t mean that death rates are going to skyrocket. In fact, with some relatively simple adaptive measures, death rates could very well go down regardless of future temperatures. That’s been the trend in the United States and should be the standard throughout all industrialized nations.

References:

Chase, T. N., K. Wolter, R. A. Pielke Sr., and I. Rasool, 2006. Was the 2003 European summer heat wave unusual in a global context? Geophysical Research Letters, 33, L23709, doi:10.1029/2006GL027470.

Fouillet, A., G. Rey, V. Wagner, K. Laadi, P. Empereur-Bissonet, A Le Tetre, P. Frayssinet, P. Bessemoulin, F. Laurent, P. De Crouy-Chanel, E. Jougla, and D. Hémon, 2008. Has the impact of heat waves on mortality changed in France since the European heat wave of summer 2003? A study of the 2006 heat wave. International Journal of Epidmiology, doi:10.1093/ije/dym253.

Schår, C., Vidale, P.L., Lu?thi, D., Frei, C., Håberli, C., Liniger, M.A., Appenzeller, C., 2004. The role of increasing temperature variability in European Summer heatwaves. Nature, 427, 332–336.




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